With the deepening of oil and gas exploration and development, the proportion of unconventional oil and gas resource exploration and development will become larger and larger. China's unconventional oil and gas resources are very rich and the exploitable resources are about (89˜126) billion tons of oil and gas equivalent, which is about 3 times of the conventional oil and gas. How to realize the efficient development of unconventional oil and gas resources is an important guarantee for national energy security, especially the unconventional oil and gas reservoirs with abundant reserves, ultra-low permeability, compactness and shale, which has great potential and has become a strategic substitute energy for conventional energy. Therefore, China regards unconventional oil and gas resources as a major area of national oil and gas development, and unconventional resource exploration and development and comprehensive utilization have become one of the current extensive research projects. Tight oil has become the most realistic unconventional oil and gas resource at present. Tight oil refers to the accumulation of oil and gas in tight reservoirs sandwiched or in close proximity to a high-quality hydrocarbon source rock system without undergoing large-scale and long-distance migration.
The efficient development of tight oil reservoirs faces the following three challenges: (1) the reservoir stratum develops micro-nano-scale pore throats, and increases the effective utilization rate of reserves, which is challenging. Tight oil reservoir pore throats are small, with a porosity less than 10%, and overburden pressure permeability less than 0.1 mD (or air permeability less than 1 mD), and 30%˜50% of movable crude oil is stored in the submicro-scale pore throats of 0.1˜1.0 μm. Due to the very poor physical properties of the reservoir stratum, it is necessary to form an effective seam network to improve the degree of pore communication by horizontal well segmental fracturing, volumetric fracturing and the like, so as to achieve effective utilization. However, the dual media system with severe heterogeneity of the matrix-seam network after fracturing exacerbates the utilization difficulty of reservoir matrix reserves. (2) due to the low pressure and low permeability of the reservoir stratum, it is challenging to increase the yield of a single well. Affected by the low pressure of the formation and low single well controlled reserves, the yield of production wells generally decrease rapidly after the initial short-term high yield; the large seepage resistance causes slow pressure transmission in the formation, and the production has the characteristics of long-term low yield, difficulty in stable production, and low cumulative oil production of a single well. (3) it is difficult to supplement the formation energy, and the improvement of the recovery ratio is challenging. The recovery degree of tight oil reservoirs relying on natural energy is generally below 10%. To increase the recovery degree of the reservoir, reservoir energy must be replenished by water injection or gas injection.
CN107353886A discloses a nanocomposite for preventing CO2 gas channeling in tight oil reservoirs, and the nanocomposite is prepared by using nano silica as a core through surface modification of a silane coupling agent, a Michael addition reaction of methyl acrylate and amidation of 3-dimethylaminopropylamine. The preparation method of the nanocomposite comprises the steps: S1, preparation of nano silica; S2, surface modification of nano silica; S3, a Michael addition reaction of modified nano silica; and S4, an amidation reaction between carbomethoxy-terminated nano silica prepared in the step S3 and 3-dimethylaminopropylamine, separation, purifying and drying, so as to obtain the nanocomposite. The nanocomposite has the CO2 response characteristic, so the nanocomposite can achieve the fluidity control and the profile improvement in the tight oil CO2 flooding process, and achieve the effect of enhancing the oil recovery ratio. However, the method is only a perfection for enhancing the oil recovery ratio process through diffusion, energization and mass transfer in the CO2 flooding process, and the effect is single. In addition, the injection of CO2 is very demanding on the ground gas injection system and gas injection equipment, the gas injection pressure is high, and the continuous injection in the field is difficult.